A statement from the Two Oceans board said it had implemented a "route diversion" after comprehensive and careful consideration.

“While this diversion affects the ultra-marathon, it effectively also negates the possibility of hosting what would have been our inaugural relay, meaning that there will be no relay race," said the statement.

"Given the constraints on numbers, we will communicate personally with all relay participants.

“The half-marathon route remains unaffected, as do the four separate start times.”

The board said it had reached the decision after “extensive discussions” with the South African Police Service, the Western Cape government, the City of Cape Town, disaster management services, Western Cape emergency medical services and the Cape Town traffic department.

The Two Oceans Marathon diversion over Ou Kaapse Weg adds significantly to the amount of climbing on the 56km route. Image: Supplied

“A roll-out plan is in place to communicate this decision regarding the alternative route taking runners through Ou Kaapse Weg and not along Chapman's Peak," it said.

“We are confident that this route deviation will still live up to the promise of our milestone 50th marathon celebrations.”

People who commented about the change on the Cape Town Runners Facebook page at first thought it was a hoax. Then they expressed disappointment about the route change with less than 24 hours to the start.